The brain space (endocranium) often represents the shape of the brain contained within the neurocranial space. Unfortunately, the brain of mammal-like reptiles (ca 220 mya) is very poorly known (3 genera) because of the lack of prepared material. The striatal complex and epiphysis of the forebrain are, respectively, believed to play an integral role in species-typical behavior and day-to-day thermoregulatory adjustments, yet the evolutionary development of these structures has not been explored. The purpose of this project is to prepare adequate fossil material in generic lines near the reptilian-mammalian transition, and to evaluate changes in brain morphology. In current preparations, it has been shown that some epiphyseal structures (parietal eye) disappear in advanced reptiles (cynodonts). The absence of parietal eyes is believed to reflect internalization of temperature regulation. The contribution of other structures (turbinals, large olfactory bulbs) remain to be evaluated with the addition of more material.